A. Field of the Invention
The present invention relates to an image information reading apparatus, especially to a scanner having a simple-structure transmission mechanism which conveys an illuminating unit and photoelectric conversion unit in different directions at the same time and same speed.
B. Description of the Prior Art
An image information reading apparatus relies on the driving mechanism to maintain a stable and fixed light path, thereby to generate high quality images. Accordingly, the driving mechanisms can be roughly classified as simple and complex. FIG. 1 shows a scanner inside a housing with a simple-structure driving device. Referring to FIG. 1, the driving mechanism as shown in FIG. 1 is simple because all the optical elements for reading information off the original sheets are installed in the same carriage 102, including straight-tube fluorescent lamp 103, an array of mirrors 106, 104, 105, and CCD line image sensor 107. When the image of a sheet is being scanned, the simple driving mechanism drives only carriage 102 mounted on support device 111 back and forth while the positions of the elements inside carriage 102 remain unchanged. When scanning, a sheet is placed on glass table 101 which is at the top of the housing. An exposure light beam emitted from straight-tube fluorescent lamp 103 is shone onto the sheet and is then reflected by the sheet. The array of mirrors 106, 104, 105 guide the light beam to CCD line image sensor 107 which converts the light beam into an electrical signal.
The advantage of the simple-structure driving mechanism is that the light path can be easily controlled because all the optical elements are fixed in the carriage. However, the trade-off is that the size of the carriage becomes very bulky, heavy, and costly. If a compact scanner is desired, the scanner can hardly be made smaller based on this mechanism. For one thing, it requires at least the length of an original sheet for the carriage to move back and forth. For another thing, if the size of the scanner is reduced, the light path must also be reduced. In that case, the half-angle of the lens in front of a CCD linear sensor must be enlarged. However, in doing so, this arrangement will influence the brightness and clarity of the reflection.
A driving mechanism of complex structure is shown in FIG. 2. FIG. 2 shows a perspective view of a scanner inside a housing. The driving mechanism is complex because it requires two driving devices, one for the light source unit and the other for the arrays of mirrors. Light source unit 202 including a straight-tube fluorescent lamp 205 and a mirror 204 is fixed on light source unit 202. Other mirrors are fixed on optical member holder 201 for guiding a light beam to CCD linear image sensor 203 which is fixed on the housing. When scanning, a sheet is placed on the glass table on top of the housing, driving device moves light source unit 202 in Y distance while optical member holder 201 follows in 1/2 Y distance to keep the same light path. The complex driving mechanism can reduce the size of a scanner. However, its structure is very complex and difficult to assemble, which will inevitably raise the manufacturing cost of the apparatus. Moreover, since light source unit 202 and optical member holder 201 are both moving while scanning images, this arrangement is more likely to increase the light deflection or color deflection of reflective images.